Valves of the kind mentioned above can be made sufficiently large and robust in order to be mounted onto pipelines which transport hydrocarbons, particularly subsea pipelines, but the invention can also be exploited in other environments and in smaller dimensions.
In the Norwegian patent application No. 860923, a ball valve is disclosed which is intended for connection with a pipeline system which conveys gas and/or oil at considerable sea depths. The valve can be demounted in a submerged state for instance for inspection or repair. Replacement of the internal vital parts can take place without any kind of extra cover and without the fluid in the pipeline leaking out during demounting, or without water from the surrounding environment being able to penetrate into the pipeline. This is achieved in that the rotatable member of the known valve comprises an upper part and a lower part. The upper part, which can be demounted from the valve housing, comprises, amongst other parts, the main packings of the valve. The lower part contains two displaceable sleeves which, when the valve can be demounted from the valve housing, comprises, amongst other parts, the main packings and two displaceable sleeves which, when the valve is open, are displaced outwards to engage with bearings in the valve housing, thereby forming a leakproof, continuous fluid passageway.
In pipeline systems there is often a need for devices which can regulate the fluid flow and likewise there is a need for the mounting of metering equipment for instance for volumetric metering of fluid flows.
Apparatus of the above-mentioned kind which are placed in a fluid flow, are subjected to considerable wear and tear and demand relatively frequent, periodical maintenance. It is desirable that maintenance can be performed quickly and that it should not be necessary to depressurize the pipeline. It is also desirable that medium from the pipeline will not leak out into the surrounding environment when maintenance takes place.